This invention relates to the hydroisomerization of waxy feeds including slack wax, Fischer-Tropsch wax, waxy raffinates, and waxy distillates to produce in a good yield a lube oil basestock or blending stock having a high viscosity index (VI).
The performance criteria for lubricants such as those used in automatic transmission fluids and passenger car engine oils has become increasingly more severe and is expected to become even more so in the future. Indeed, it is expected that additive technology will be insufficient to meet future lubricant performance criteria. Thus, improved base oils will be needed.
It is generally accepted that formulators of automatic transmission fluids and passenger car engine oils will need lube oil basestocks that have a high viscosity index (VI) and a low paraffinic wax content.
Isomerization of wax and waxy feeds to liquid products boiling in the lube boiling range is a practice well-known in the art. Catalysts useful in such processes comprise Group VIII metals on refractory oxide support such as silica-alumina and acidic refractory metal oxide supports such as fluorided alumina. Catalysts using silica-alumina supports are known to produce isomerates with good viscosity index; however, these materials traditionally exhibit poor selectivity for wax disappearance into isomerate product with the result that the yields of the isomerate lube are low. In the case of catalyst supported by halogenated aluminas such as fluorided alumina high VI isomerates are produced; however, the activity of these catalysts is low thereby requiring higher temperatures and pressures to process the feed which is generally undesirable. As a consequence, there remains a need for catalysts and processes which will produce good yields of lube basestocks with high VI.
This invention relates to a method of producing a lube oil feedstock from a waxy feed which comprises: contacting the waxy feed with an isomerization catalyst under catalytic isomerization conditions wherein the isomerization catalyst comprises a metal hydrogenation component and a silica-alumina support, said silica-alumina having a pore volume of less than 0.99 ml/gm (H2O), an alumina content of between about 35 to 55 wt % based on silica-alumina and an isoelectric point of from 4.5 to 6.5 to provide a lube feedstock; and thereafter solvent dewaxing at least a portion of the feedstock.
This and other embodiments of the invention will be discussed below.